Everyday Tech From Space: How GPS Systems Help People Navigate

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While driving in an unfamiliar city, most
people take the instructions from their Global Positioning System
(GPS) device for granted — never pausing to wonder how the
disembodied voice knows their destination is just two left turns
away.

But GPS, in fact, is a marvel of space-based technology.
The GPS
receivers in cars and smartphones calculate locations,
velocities and directions based on signals pinged out by a
constellation of 24 satellites orbiting thousands of miles above
Earth.

GPS began its life as a
strictly military technology, and to this day the United
States Air Force operates and maintains the satellites. But GPS
has now flooded into the everyday lives of billions of people
around the world, letting them know where they are at any moment
— and how to get to a better place.

Military roots

The Air Force maintains a constellation of at least 24
working GPS satellites, each orbiting about 12,500 miles (20,117
kilometers) above the Earth's surface. These satellites, which
circle the planet every 12 hours, emit continuous navigation
signals.

Receivers on the ground snag these signals out of the air,
using them to calculate time, location and velocity with high
accuracy. The technology has also found its way into
many spheres of modern life, helping scientists mark their
field sites and assisting delivery companies in tracking
packages.

The roots of GPS technology date back to World War II, when
the U.S. and British navies deployed navigation systems that used
ground-based radio signals. But the idea really got off the
ground when the Soviet Union launched
Sputnik — the world's first artifical satellite — in
1957.

Just days after Sputnik's launch, American scientists
noticed that they could pinpoint the satellite's location based
on the Doppler shift of its radio signals — a measure of how the
wavelengths seemed to stretch out or contract depending on the
satellite's movements.

This got the researchers thinking about creating a
space-based navigation system. In the late 1950s, they began
developing and testing satellite navigation technology, and the
U.S. Navy deployed the operational Transit satellite system in
the 1960s.

Then, in 1973, a group of Pentagon officials decided to
create a "defense navigation satellite system," laying the
groundwork for a system called Navstar-GPS — what we now know
simply as GPS.

Getting up to speed

The U.S. Air Force sent the first GPS satellite into orbit
in 1978, and many other launches followed over the years.

By the early 1990s, the system was functioning, and its
capabilities were demonstrated during the first Gulf War. Allied
troops relied heavily on GPS to navigate the featureless Arabian
desert, Air Force officials have said. By 1995, the 24th GPS
satellite was in position, marking the system's arrival at full
operational capacity.

GPS satellites send out two signals — one for military use
and one for civilian applications. In the early years, the
civilian signal was intentionally degraded for national security
purposes. But that changed in 2000, when President Bill Clinton
ordered the degradation turned off, making civilian GPS much more
accurate. The decision has helped GPS become a more reliable tool
for private citizens all over the world.

The capabilities of GPS are constantly improving, as the
Air Force launches
newer, more accurate GPS satellites on a regular basis. The
U.S. federal government is committed to providing a minimum of 24
operational GPS satellites on orbit, 95 percent of the time.
There are currently more than 30 satellites up, providing some
margin for error.

While GPS is the most widely used system around the world,
it's not the only space-based navigation network out there.
Russia has its Glonass system, for example, which the Soviet
Union began to devise back in the 1970s.

The European Union is planning a navigation system called
Galileo, and China has already launched multiple satellites for
its
Beidou ("Compass") system, which it hopes to have operational
by 2012.

While driving in an unfamiliar city, most
people take the instructions from their Global Positioning System
(GPS) device for granted — never pausing to wonder how the
disembodied voice knows their destination is just two left turns
away.

But GPS, in fact, is a marvel of space-based technology.
The GPS
receivers in cars and smartphones calculate locations,
velocities and directions based on signals pinged out by a
constellation of 24 satellites orbiting thousands of miles above
Earth.

GPS began its life as a
strictly military technology, and to this day the United
States Air Force operates and maintains the satellites. But GPS
has now flooded into the everyday lives of billions of people
around the world, letting them know where they are at any moment
— and how to get to a better place.

Military roots

The Air Force maintains a constellation of at least 24
working GPS satellites, each orbiting about 12,500 miles (20,117
kilometers) above the Earth's surface. These satellites, which
circle the planet every 12 hours, emit continuous navigation
signals.

Receivers on the ground snag these signals out of the air,
using them to calculate time, location and velocity with high
accuracy. The technology has also found its way into
many spheres of modern life, helping scientists mark their
field sites and assisting delivery companies in tracking
packages.

The roots of GPS technology date back to World War II, when
the U.S. and British navies deployed navigation systems that used
ground-based radio signals. But the idea really got off the
ground when the Soviet Union launched
Sputnik — the world's first artifical satellite — in
1957.

Just days after Sputnik's launch, American scientists
noticed that they could pinpoint the satellite's location based
on the Doppler shift of its radio signals — a measure of how the
wavelengths seemed to stretch out or contract depending on the
satellite's movements.

This got the researchers thinking about creating a
space-based navigation system. In the late 1950s, they began
developing and testing satellite navigation technology, and the
U.S. Navy deployed the operational Transit satellite system in
the 1960s.

Then, in 1973, a group of Pentagon officials decided to
create a "defense navigation satellite system," laying the
groundwork for a system called Navstar-GPS — what we now know
simply as GPS.

Getting up to speed

The U.S. Air Force sent the first GPS satellite into orbit
in 1978, and many other launches followed over the years.

By the early 1990s, the system was functioning, and its
capabilities were demonstrated during the first Gulf War. Allied
troops relied heavily on GPS to navigate the featureless Arabian
desert, Air Force officials have said. By 1995, the 24th GPS
satellite was in position, marking the system's arrival at full
operational capacity.

GPS satellites send out two signals — one for military use
and one for civilian applications. In the early years, the
civilian signal was intentionally degraded for national security
purposes. But that changed in 2000, when President Bill Clinton
ordered the degradation turned off, making civilian GPS much more
accurate. The decision has helped GPS become a more reliable tool
for private citizens all over the world.

The capabilities of GPS are constantly improving, as the
Air Force launches
newer, more accurate GPS satellites on a regular basis. The
U.S. federal government is committed to providing a minimum of 24
operational GPS satellites on orbit, 95 percent of the time.
There are currently more than 30 satellites up, providing some
margin for error.

While GPS is the most widely used system around the world,
it's not the only space-based navigation network out there.
Russia has its Glonass system, for example, which the Soviet
Union began to devise back in the 1970s.

The European Union is planning a navigation system called
Galileo, and China has already launched multiple satellites for
its
Beidou ("Compass") system, which it hopes to have operational
by 2012.